Project summary. Health disparities are a matter of grave public health significance10, and advancing scientific understanding of the causes of health disparities is part of the National Institute of Minority Health Disparities strategic plan. Racial health disparities have complex etiologies and correlates, but remain when controlling for other social determinants of health11 and patient factors such as treatment refusal12. Residual disparities reflect differences in provider treatment of White and minority patientse.g.13?15. One factor contributing to disparate treatment of minority patients is provider implicit bias?non-conscious biases that alter behavior16. Provider implicit bias predicts subtle behavioral differences in interactions with minority patients, including more anxiety-related word usage17, more negative affect18, and different nonverbals19. These provider behaviors predict lower patient satisfaction and adherence20, with health and mortality consequences20,21. Despite haste to target implicit bias in disparity reduction interventions, the research on implicit bias reduction efforts is weak and mixed; most studies show no impact of implicit bias interventions19. Furthermore, implicit bias is difficult to measure and demonstrates only moderate test-retest reliability22. Nevertheless, there are clear public health implications of even weak effects of implicit bias23 when considering the number of people affected. Effects of implicit bias on disparities may be clarified by articulating and examining more complex models of the relationship between implicit bias and provider behavior. This proposal examines intergroup anxiety (anxiety that manifests in interracial interactions in response to negative expectations24) as a mediator of the relationship between implicit bias and provider behavior. It is well known that anxiety affects behavior in the general populatione.g.25, and provider anxiety impairs patient outcomes, such as satisfaction and adherence26,27, but no research has examined the effects of intergroup anxiety on provider behavior. To ensure a comprehensive analysis of the innovative association between intergroup anxiety and provider behavior, we propose to measure both constructs at multiple levels. We will assess anxiety through both self-report affect and physiology28. We will examine three classes of behavior: verbal behavior (anxiety-related word use), global behavior (warmth) and nonverbal behaviors (using indicators identified by expert tape analysis?recent pilot, and aim 1). We will conduct this research in medical students (N=70). Medical school is a key window-of- opportunity when biases may be more malleable29, students are accessible, and training is expected. Many medical schools use implicit bias reduction trainings to decrease disparities, but intergroup anxiety may represent a more consistently alterable and easy-to-measure construct. Disparity-reduction trainings based on evidence-based models such as the proposed may have large impacts on health disparities; my long-term career goal is to study factors that contribute to health disparities across multiple social determinants of health and design, test, and disseminate interventions on evidence-supported targets such as intergroup anxiety.